Infrared heater



APIil 11, 1967 H. MoHN ETAL 3,313,921

' INFRARED HEATER I Filed Nov. 6, 1965 2 Sheets-Sheet 1 ngz NVEIITOAS!xfs/mm MoH/v, GEORG HoRsrMM/v) Baak/mko Mu'iLR April 1,1 1967 H. MoHNl-:TAL 3,313,921

INFRARED HEATER Filed Nov. 6, 1965 2 Sheets-,Sheet 2 lNVEa/ros:

IIE/#RICH Molina GEORGHoRSrMA/VN) EERIMRD MULJER Treff/vifs UnitedStates Patent O 3,313,921 INFRARED HEATER Heinrich Mohn, Hailer, GeorgHorstmann, Eruchkohel, near Hanau am Main, and Eberhard Muller, Hanau amMain, Germmy, assignors to Heraeus Quarzschmelze G.m.b.H., Hanau amMain, Germany, a German trm File-'l Nov. 6, 1963, Ser. No. 321,950Claims priority, application Germany, Nov. 16, 1962, H 47,417; Mar. 12,1963, H 48,501 3 Claims. (Cl. 2MP- 553) The present invention relates toan electric infrared heater having an electric heating conductor Withina tube of quartz glass, vitre-ous silica ware, refractory glass, or thelike, and elect-ric connections for said heating element at one end ofsaid tube.

There are different designs of electric infrared heaters of theabove-mentioned type already known. The heating conductor of these knowninfrared heaters usually consists of a wire or wire coil which is woundon the out-side of a supporting tube from the inlet end thereof, and theother end of the conductor then runs from the other end of thesupporting tube through the inside of this tube back to the inlet endwhere the electric connections for two ends of the conductor arelocated. These infrared heaters have the disadvanta-ge that the part ofthe heating conductor which extends along the insi-de of the supportingtube is excessively heated during the operation of the heater which isdue to the fact that` aside from its own heat, this inner part alsoyreceives a considerable additional heat from t-he part which is woundupon the outside of the supporting tube and that the heat of this innerpart cannot be freely radiated therefrom. Due t-o the excessive thermalload on this part of the heating conductor extending along the inside ofthe supporting tube, this part becomes highly incandescent and easilyburns through.

There is another type of infrared heaters known which also has it-selectric connections at one end thereof and in which the heatingconductor is provided in capillary tubes in a solid body of quartz glassor vitreous silica ware which may also be formed by sintering ormelting. Such infrared heaters have the disadvantage that they. arerather bulky and that in the operation of the heater the solid body ofquartz glass or the like is not heated uniformly so that thermalstresses occur which may result in fissures and cracks in this bodywhich in serious cases may `even end in bursting and destruction of theentire heater. Due to the relatively large bulk. of the heater, there isalso the danger that heat accumulations may form therein which mayimpair the heating conductor. These infrared heaters with capillarytubes have the further very serious disadvantage that they canbeproduced only at a very considerable expense.

It is an object of t-he present invention to provide an infrared heaterof the type in which the heating conductor is mounted within an outertube of quartz glass, vitreous silica ware, refractory glass or the likeand the electric connections for the heating conducto-r are provided atone end of this tube, and which is designed so as to overcome all of theabove-mentioned disadvantages of similar infrared heaters in anextremely simple manner. According to the invention, this is attained byproviding a thin strip of an electrically insulating material,preferably quartz glass, vitreous silica ware, refractory glass or thelike, at the inside of the outer tube and spaced at a short distancefrom the inner wall thereof so as to form a partition in this tube, andby inserting the heating conductor into the chambers which are formed inthe tube by this partition. The insulating strip is made of very smallthickness in comparison to its length. The heating con- `thickness ofonly 1 mm.

3,313,921 Patented Apr; 11, 1967 lCC ductor which is located in the twochambers may then radiate its heat freely and there is no danger as inthe infrared heaters of the known type that the parts of the heatingconductor or the supporting part might become excessively heated or thatheat accumulations or uneven heating of the heater parts might occur. Ifthe insulating strip as well as the outer tube are made, for example, ofopaque quartz glass, a very uniform heating effect will be attainedsince the insulating strip permits the infrared radiation of the heatingconducto-r to pass through it very well up to about 4p because of thegood permeability of quartz within the infrared wave ran-ge. By beingmade of the same material, the outer tube and the insulating strip havethe same coefficient of thermal expansion. Quartz glass, vitreous silicaware, or lrefractory glass are especially suitable materials for makingthe insulating vstrip because of their good elasticity and electricinsulating effect. Another advantage of the invention also consists inthe fact that the insulating strip with the heating conductor thereonmay be inserted in a very simple manner and without danger of breakageinto the Outer tube, even if it has a length of, for example, l m. and aThe insulating strips may also be easily produced at a low expense,`forexample, by extrusion. This if of considerable importance sinceinfrar-ed heaters are articles of which very large amounts are requiredin industry and which therefore should be m-ade by method-s of massproduction. The infra-red heater according to the invention thereforenot only overcomes all of the technical disadvantages of the infraredheaters of a simi-lar type which were previously known, but itsIradiation properties are also superior and its manufacture isconsiderably more simple and inexpensive than that of the known heaters.

The above-mentioned as well as various additional features andadvantages of the present invention will becom-e more clear-ly apparentfrom the following detailed description thereof which is to be read withreference to ,the accompanying drawings, in which FIGURE l shows aperspective view of an infrared heater according to the inventi-on;l

FIGURE 2 shows a cross section which is taken along line II-II of FIGURE1;

FIGURE 3 shows a similar cross section of an infrared heater accordingto a modification of the invention;

FIGURE 4 shows a longitudinal section of an infrared heater according toa further modication of the invention; while f FIGUR-E 5 shows a crosssection which is taken along line VV of FIGURE 4.

Referring rst to FIGURES 1 and 2 of the drawings, the infrared heateraccording to the invention consists of an outer tube 1 of quartz glass,vitreous silica ware, refractory glass, or similar material, into theopen end of which an insulating strip 2 of a similar material isinserted on which a heating conductor in the form of a wire coil ismounted, the two parts 5, 5 of which extend along the opposite sides ofthe insulating strip 2 within two equal chambers 3 and 4 which areformed by strip 2 at the inside of tube 1. This strip 2 preferably has awidth only slightly smaller than the inner diameter of tube 1 and itslower end is provided with a slot 6 in which the straight connectingpart between the two coiled parts 5 of the heating conductor is held.The lower end of the insulating strip 2 is preferably held in positionnear the closed end of tube 1 by a wad of quartz wool 7. The free upperends 8 and 9 of the heating conductor are to be connected to a source ofcurrent.

FIGURE 3 shows a modification of the invention, in which the insulatingstrip has a cross-shaped cross section so as to form four equal blades10, 11, 12, and 13.

By the insertion of this insulating strip, four equal charnbers 14, 15,16, and 17 are formed at the inside of tube 1 in which two separateheating conductors 18 and 19 may be located which may be separatelyconnected to a source of current. Of course, it is also possible toemploy a single heating conductor which is passed twice back and forthalong the insulating strip within the four chambers 14 to 17.

The infrared heater either according to FIGURES 1 and 2 or according toFIGURE 3 may be further improved in the manner as illustrated in FIGURES4 and 5 by twisting the flat insulating strip 2 or, in a similar manner,the cross-shaped strip to 13 accordin-g to FIGURE 3 about itslongitudinal axis. This has the advantage that the heating coil or coilswill be held more securely in the proper position so that, even afterthe heater has Ibeen used for a long time in a perpendicular positionand even though it may have a length of 1 m. and more, the coil or coilswill be absolutely prevented from sagging or from becoming distorted.Furthermore, the radiation of this infrared heater will be even moreuniformly distributed n all directions than that of the heatersaccording to FIGURES 1 to 3, especially if the heating conductorconsists of two equal heating coils which are passed back and forth.yEven in the particular case when the heating conductor consists of twounequal parts, for example, of a heating coil and a straight return wirewhich are separated from each other -by the twisted insulating strip, auniform distribution of the radiation in all directions will beatta-ined.

The inventive arrangement of a Hat insulating strip which is eitherstraight or twisted or of an insulating strip with intersecting blades,either straight or twisted, within the tube of an infrared heater hasproved especially successful if the tube has an inner diameter of 6 to16 mm. into which an insulating strip of a thickness of about 0.8 to 1.5mm. and a width of slightly less than the inner diameter of the tube isinserted. If the insulating strip, either at or with intersectingblades, is twisted, each spire preferably has a len-gth of 3 to 5 cm.The heating conductor preferably consists of a heating coil passingalong the chambers which are formed by the insulating strip, and it ispreferably made and supplied with current so that the infrared heaterhas an output of about 4 to 7 mm. into which an insulating strip of athickness of about A s can be appreciated by the artisan, the advantagesof the invention proceed from using a partition member support structureand outer tube container for the electrically energized infraredradiation generating elements which assure a substantially freeinterchange of radiant `energy emitted by the various generatingelements and portions thereof. This results in a uniformomni-directional distribution of the generated radiation whicheliminates differential thermal stresses and hot spots that could damagethe tube or even the generating elements themselves, as in certain priorart infrared heaters. To achieve such a favorable radiationdistribution, the outer tube as well as the partition member and itsvarious blades are made of a material, preferably quartz which issubstantially transparent to infrared radiation.

Of the various other materials which can be used for makin-g thepartition member and outer tube are vitreous silica wear, refractoryglasses and similar materials. These materials can be, and in certainapplications preferably are opaque to visible light radiation, as forexample, opaque quartz glass, since in a infrared heater, it is theinfrared radiation transmission characteristics which are impogtant.Therefore, it is most advantageous to,

make the partition member and outer tube from a material such as opaquequartz glass which is substantially transparent to infrared radiation upto a wave length of approximately 4 microns. By excluding transmissionof visible light radiation generated incidentally by the heaterelements, the radiation output of the heater can be made substantiallypure infrared.

Although our invention has been illustrated and described with referenceto the preferred embodiments thereof, we wish to have it understood thatit is in no way limited to the details of such embodiments, but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed our invention, what we claim is:

1. An infrared heater comprising an elongated outer tube of quartzhaving an open end and a closed end, an electrically insulatingpartition member substantially transparent to infrared radiation anddefine-d by an elongated strip twisted about its longitudinal axis todivide the interior of said tube into two adjacent convoluted chambers,an electrical resistance heating element disposed within V each of saidconvoluted chambers for extension along the length thereof andcontainment thereby, said resistance heating elements being electricallyconnected in series at the close-d end portion of said tube and disposedfor connection at the open end portion of said tube to an eX- ternalsource of electrical energy for heating thereby to generate infraredradiant energy for transmission from and through said tube, and supportmeans disposed within said tube at the closed end portion thereof tosupport said twisted strip partition member in an endwise separatedrelation to the closed end of the tube.

2. The infrared heater according to claim 1 wherein said support meansincludes a wad of quartz wool disposed within said tube at the closedend thereof to define a support cushion for the end of the twisted strippartition member adjacent thereto.

3. The infrared heater according to claim 1 wherein said outer tube andtwisted strip partition member are made of opaque quartz glass which issubstantially transparent to infrared radiation of wave length up toapproximately 4 microns.

References Cited by the Examiner UNITED STATES PATENTS 1,437,481 12/1922Armstrong 219--523 1,894,887 1/1933 Pingrey 219-335 X 1,918,078 7/1933Apple 3'38-235 1,995,000 3/1935 Hyatt 219-335 X 2,224,422 12/ 1940Ballman 3318-241 X 2,554,745 5/1951 `Kapsch 219-523 X 2,703,833 3/1955Vanvor 338--33 2,715,675 8/1955 Macksoud 338-268 X 2,824,199 2/1958Browne 338-241 X 2,844,694 7/ 1958 Lefebvre 338-236 3,107,290 10/1963Willinger 219-523 X FOREIGN PATENTS 498,254 10/ 1919 France. 1,143,6054/ 1957 France.

714,436 8/ 1954 `Great Britain. 838,101 7/ 1960 Great Britain.

ANTHONY BARTIS, Primary Examiner.

RICHARD M. WOOD, Examiner. Y. Y. MAYEWSKY, Assistant Examiner.`

1. AN INFRARED HEATER COMPRISING AN ELONGATED OUTER TUBE OF QUARTZHAVING AN OPEN END AND A CLOSED END, AN ELECTRICALLY INSULATINGPARTITION MEMBER SUBSTANTIALLY TRANSPARENT TO INFRARED RADIATION ANDDEFINED BY AN ELONGATED STRIP TWISTED ABOUT ITS LONGITUDINAL AXIS TODIVIDE THE INTERIOR OF SAID TUBE INTO TWO ADJACENT CONVOLUTED CHAMBERS,AN ELECTRICAL RESISTANCE HEATING ELEMENT DISPOSED WITHIN EACH OF SAIDCONVOLUTED CHAMBERS FOR EXTENSION ALONG THE LENGTH THEREOF ANDCONTAINMENT THEREBY, SAID RESISTANCE HEATING ELEMENTS BEING ELECTRICALLYCONNECTED IN SERIES AT THE CLOSED END PORTION OF SAID TUBE AND DISPOSEDFOR CON-A NECTION AT THE OPEN END PORTION OF SAID TUBE TO AN EXTERNALSOURCE OF ELECTRICAL ENERGY FOR HEATING THEREBY TO GENERATE INFRAREDRADIANT ENERGY FOR TRANSMISSION FROM AND THROUGH SAID TUBE, AND SUPPORTMEANS DISPOSED WITHIN SAID TUBE AT THE CLOSED END PORTION THEREOF TOSUPPORT SAID TWISTED STRIP PARTITION MEMBER IN AN ENDWISE SEPARATEDRELATION TO THE CLOSED END OF THE TUBE.